In a refrigeration cycle of an air-conditioning apparatus, refrigerant liquid condensed in a condenser is depressurized by an expansion valve and flows into an evaporator in a two-phase gas-liquid state in which refrigerant vapor and refrigerant liquid coexist. When refrigerant flows into the evaporator in two-phase gas-liquid state, in the case of a vertical or inclined header, energy efficiency of the air-conditioning apparatus is decreased due to factors including degraded distribution characteristics with respect to a heat exchanger. Also, due to changes in a flow rate condition such as a high flow rate condition and low flow rate condition, stable distribution characteristics cannot be maintained.
Thus, to improve distribution characteristics, some conventional heat exchangers have a partition installed or a ribbon-shaped turbulence accelerator or a small hole installed in the vertical or inclined header (see, for example, Patent Literature 1).